Apparatus for and method of screening pulp



24 19270 Ma} J. w. STEVENS APPARATUS FOR AND METHOD OF SCREENING PULP 1926 2 Sheets-Sheet 1 Filed June 12 INVENTOR firfy W. Sieve/7s f 3. 0

ATTORNEYS I 1 May 927 J. w. STEVENS APPARATUS FOR AND I IETHOD 0F SCREENING PULP Filed June 12, 1926 2 Sheets-Sheet 2 INVENTOR Jerry W J/evms ATTORNEYS Cal Patented May 24, 1927.

' unrrsn STATES 1,529,812 PATENT orrics.

JERRY W. STEVENS, OF CLOQUET, MINNESOTA, ASSIGNOR TO NORTHWEST PAPER COMPANY, OF CLOQUET, MINNESOTA, A CORPORATION OF MINNESOTA.

APPARATUS FOR AND METHOD OF SCREENING PULB.

Application filed Jime 12, 1926. Serial No. 115,483.

This invention relates to an apparatus for screening pulp and specifically to a method for washing the screens to prevent cloging.

Among the objects of myinventionare the following;

Eliminating the labor necessary to kee inclined flat pulp screens from clogging, eliminating the wear of the screens which results from use of mechanical scrapers, securing uniform screening and eliminating interruption of the suction on the screens, eliminating the'use of the excessive quantities of water necessary with present day mechanically operated movable sprays, eliminating the localized erosion of screens when stationary sprays are used.

Other objects and advantages of my invention will become clear from'the following description and the appended drawings,

screening the shives out of pulp and are made in the usual manner well known to those skilled in the art. Fig; lis a side elevation of a ty ical three section flat screen. The screen 1, s own by a dotted line in Fi 1 inclines from the upper or left hand end, where the suspension of pulp in water is fed onto the screen, to the lower or right hand discharge end where the coarse particles or shives are dischar ed. The screens are usually made of slotted metal, the slots running parallel to the long way of the screen as indicated diagrammatically in Fig. 2. The screen is mounted in a suitable box 2 as shown in Fig. 3. The bottom of the box is provided with means for maintaining a suction on the flat screens and means for carrying oil the screened stock in water suspension. A rubber diaphra m 3, fastened to the bottom edges of ox 2 and gripped between two suitable plates 4 and 5, is actuated perpendicularly by a connectbeing fed to the screens.

ing rod 6 driven by a ca-m'7 on a shaft& The reciprocating perpendicular motion of the rubber diaphragms in the enclosed box, as explained hereinafter, creates a suction on the dotted screen and speeds up the screening action. Each of the three sections of screen 1 is similarly equipped. The water suspension of pulp passes through screen 1, the shives remaining on the screento be discharged at the lower or right hand end.. By suitable discharge openings the water suspension of pulp passes from box 2 between the screen and rubber dia hragrn into the trough 9. This trough is deep enough to prevent the suction from pulling air t rough the opening at the bottom into the chamber under the screen. The water suspension of screened pulp in the trough 9 is then ready to be pumped or otherwise contains a small proportion of pulp, which may be about one pound per 30 gallons of water, so that its mobility is about that of water. Although the first section of screen removes its proportionate share of ulp and water flowing over it there is no ten ency for this screen to clog with shives due to the large excess volume of water and pulp passing over it. In the second section, the suspension thickens perceptibly though this is governed by the amount of water suspension If this is large, clogging does not take place except at its lower end. There is liable to be considerable clogging of the third section, unless special expedients are resorted to. As the fine pulp and water pass through the screens the shives pile up on the screen surface and. clog the screen slits. If enough pulp, suspension is fed onto the screen so that an excess is discharged at the lower end, thereby keeping all three screen sections from clogging, the efficiency of the operation is decreased because the oversize dischar e contains undersize fibers in addition to s ives. It is therefore necessary to operate the screens so that practically all of the water is removed before reaching the discharge end. If the shives are not removed mechanically or flushed ofl the screen, they accumulate on and clog the screen and cut down its capacity. It therefore becomes necessary to remove the shives almost continuously from the screen. Many mechanical devices have been used to supplant hand flushing and raking but all of these have some objections. A water spray in the hands of a man is an excellent method for keeping the screens clear but the labor cost is considerable. My invention closely simulates hand spraying and it is to this that I attribute its success when used in actual paper mill operations.

My preferred embodiment is as follows: A spray head 12, as shown in Fig. 4, 1s

mounted on a pipe 13, and water is supplied.

to the spray head through this pipe. I prefer to make the spray heads with two openings so that the water is sprayed in opposite directions parallel to the flow of the water suspension on the screen. These openings may well be in the form of slots 12 and 12" parallel'to the screen surface. Furthermore, spray heads delivering water in the opposite direction to the flow of the stock tend to retard the flow, thus separating the fibers from the screenings, and permitting the fibers to pass down through the screen plate slots more readily, and hence increasing the capacity of the screens. While spray heads with one opening may be used this requires doubling their number and increases the cost to effectively spray substantially the entire surface of that section of the screen that is within range of the spray. The pressure of water in the spray head should be hi h enou b so that the spray of one head su stantlally reaches the spray of the next. Control valves 15 regulate the individual spray heads.

The pipes 13 are suitably spaced along a header ipe 14, which is centrally located above t e long axis of the screen 1. The header pipe 14 furnishes the water to the spray head pipes 13. In the drawings, the spray heads are closer together in the third section than in .the second, because of the necessity for more flushing, due to a greater accumulation of shives on the screen. A flexible hose 16 connects the header 14 to the water supply.

The header pipe 14 is mounted in bearings 17, such as simple pillow blocks, so that it is free to turn. Thebearings are supported on braces 18, which may be made of strap iron, the braces being preferably supported b the sides of screen box 2. Theheader pi e 14 has an arm 19 attached to it drilled Wlth holes as shown in Fig. 3. This arm is connected by a suitable drive rod 20 to a crank 21 connected by a suitable series of gears 22 and belt pulley 24 or other mechanism to a source of power such as the cam The spray heads are mounted so that the. sprays are perpendicular to the plane of reciprocation.

While I have described my referred embodiment I do not wish to be llmited to this specific mechanism. Other mechanism capable of reciprocating the spray heads across the screen and known to those skilled in the art may be used. Other types of spray heads and screens may also be used to carry out my invention.

The reciprocation of the sprays over the surface of the screen in the manner described subjects substantially the entire surface of the screen Within range of the sprays to an intern'iittent washing by fresh Water. I have found that in actual practice these sprays have little tendency to break the suction on the screens, a difliculty which is often encountered with other types of screen clearing apparatus.

I claim:

1. In a mechanism of the character described, the combination of a screen over which the water suspension passes, a water spray device above the screen made up of a p urality of spray-heads spaced at intervals along the direction of flow of the water suspenslon on the screen each of said sprayheads being provided with two openings to direct the water in opposite directions parallel to the flow of pulp in water suspension on said screen, means for reciprocating said spra -heads across the screen in a plane perpen icular to the flow of the water suspension, and means for supplying water to said spray-heads.

2. In a mechanism of the character described, the combination of a screen over which the water suspension passes, a waterspray device above the screen made up of a plurality of spray-heads spaced at intervals along the direction of flow on the screen for spraying water in opposite directions parallel to the flow on the screen, means for reciprocating said spray-heads in an arc across the screen in a plane perpendicular to the flow of the water sus ension, and means for sugpliying water to said spray-heads.

n a pulp screening ap aratus, the combmation of a screen over w ich pulp in water suspension passes, receiving boxes underneath the screen, means for reci rocating water sprays across the surface of t e screen in a plane perpendicular to the flow of the pulp suspension along the screen, said reciprocating sprays being placed at intervals along the surface of the screen to direct said water s rays along the surface of said screen perpen icular to the reciprocating plane and each of said spray-heads being provided with two openings to direct the water in opposite directions parallel to the flow of pulp in water suspension on said screen.

4. In a pulp screening apparatus, the com-= bination of a screen over which pulp in wa ter suspension passes, receiving boxes underneath the screen with means for applying suction to the screen, means at intervals along the surface of the screen to direct water sprays in opposite directions parallel to the direction of flow of the pulp suspension, means for reciprocating said Water sprays across the screen surface to subject substantially the entire surfaceof the screen within range of the sprays intermittently to the action of water spray.

5. Apparatus for screening pulp comprising in combination a plurality of suction boxes, a screen above said boxes for receiving pulp to be screened, spray heads mount ed on movable means above said screen for directing Water sprays along the upper surface of said screen, said spray heads each having two openings to direct the water in opposite directions parallel to the flow of the pulp in Water suspension on the screen, said spray heads being mounted on pipes so connected as to furnish water to the spray heads, said pipes being so suspended that the spray heads swing in arcs directly above the screen and in a plane at right angles to the flow of the suspension on the screen, mechanism for moving said pipes, said sprays being spaced to subject substantially the entire screen surface within range of the sprays intermittently to the washing action of water spray from the spray heads.

6. Apparatus for screening pulp comprising a screen over which the pulp in water suspension passes, spray-heads arranged at intervals along the upper surface of the screen, said spray-heads being provided with two openings to direct the water in opposite directions parallel to the flow of the pulp in water suspension on the screen, and means for oscillating said spray-heads transversely of the screen.

7. The method of screening pulp in water suspension which comprises discharging said pulp suspension onto an inclined screen at one end thereof, directing sprays of water into the flowing pulp suspension in opposite directions parallel to the direction of flow, reciprocating said sprays slowly across the surface of the screen in a plane perpendicular to the flow of the pulp suspension, and subjecting substantially the entire sur face of the screen within range of the sprays intermittently to the action of said water sprays.

8. The method of preventing clogging of pulp screens which comprises directing spraysof water over the surface of the screen parallel to the axis of flow of the pulp on said screen and in opposite directions; and reciprocating said sprays across the screen in a plane perpendicular to the flow of the suspended pulp to subject substantially the entire screen surface within range of the sprays to intermittent spraying.

9. The method of facilitating the screening of pulp in water suspension While flowing over an inclined screen, which comprises directing sprays of water against the flowing pulp suspension to help separate the fibers from the screenings, said sprays reciprocating slowly across the surface of the screen in a plane perpendicular to the flow of the pulp suspension the alternate sprays extending in opposite directions.

In testimony whereof I aflix my signature.

JERRY W. STEVENS. 

